Seven of Nine is sent back in time to stop an explosion.
The twenty-ninth-century timeship Relativity, under Captain Braxton, is trying to stop a bomb planted on Voyager. Braxton's crew pull Seven of Nine out of time moments before Voyager is destroyed, because her Borg senses can detect the device. Disguised as an ensign, she goes to the shipyard where Voyager is being readied for launch and finds the bomb, but the trip back kills her, so a slightly earlier Seven is sent to the period when the ship was fighting the Kazon.
There Janeway, who remembers her from the shipyard, captures her, and together they learn that the saboteur is a future Braxton, who blames Voyager for his years stranded in the twentieth century. Seven, worn down by time travel, chases him to the day of the blast, and a recruited Janeway stops him in the past. Lieutenant Ducane arrests Braxton and returns the two women to their time. The fifth-season puzzle revisits Voyager's past and follows up on Future's End.